In the course of further development of mobile radio communication systems, work is currently being undertaken to replace the mobile radio communication systems based on the GSM (Global System for Mobile Communications) standard with the more powerful mobile radio communication systems based on the UMTS (Universal Mobile Telecommunication System) standard.
Since the network coverage achieved using UMTS mobile radio networks, that is to say mobile radio communication systems based on the UMTS standard, is not yet as far advanced as the network coverage achieved using the existing GSM mobile radio networks, that is to say mobile radio communication systems based on the GSM standard, it is possible to use UMTS mobile radio networks only in particular geographical areas for communication services, while other geographical areas have only GSM mobile radio networks available. Accordingly, the situation may arise in which a user of a mobile radio subscriber appliance is using a GSM mobile radio network to use a communication service and moves into the domain of a UMTS radio cell, that is to say into a geographical area in which a UMTS mobile radio network can be used, and, because the reception quality of the UMTS mobile radio network is higher there than the reception quality of the GSM mobile radio network, for example, or because a higher data rate can be achieved in the communication service when using the UMTS mobile radio network, the user now wishes to use the communication service using the UMTS mobile radio network, or because the user wishes to use a communication service which is provided only by means of the UMTS mobile radio network.
A change of mobile radio network used to provide a communication service or to provide a communication link is called inter-system handover of the communication service or of the communication link. In the described case of a change from a GSM mobile radio network to a UMTS mobile radio network, this is specifically inter-system handover from a GERAN (GSM EDGE Radio Access Network; EDGE: Enhanced Data Rates For GSM Evolution) to a UTRAN (Universal Terrestrial Radio Access Network).
When a communication service is provided using a packet-switched communication link, for example when the communication service involves allowing a user to transmit data between the user's mobile radio subscriber appliance in the Internet, handover is referred to as packet-switched handover for the communication service or the communication link.
In the case of inter-system handover for a packet-switched communication link, that is to say packet-switched inter-system handover, from a GERAN to a UTRAN, it is necessary for the UTRAN, that is to say the radio access network of the UMTS mobile radio network, to have some information specific to the mobile radio subscriber appliance in order to be able to perform the inter-system handover.
This information is defined in the RRC (Radio Resource Control) container INTER RAT HANDOVER INFO, which contains the RAC (Routing Area Code) for the mobile radio subscriber appliance and the parameter START PS, an input parameter which is stored on the USIM (Universal Subscriber Identity Module) for the encryption algorithm used in the PS (packet-switched) domain, see 3GPP TS 25.331; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 5).
This information, which is subsequently called the required information, needs to be available in the UTRAN, that is to say in an RNC (Radio Network Controller) for the UTRAN, no later than when a GERAN node, that is to say a BSC (Base Station Controller) for the GERAN, requests the inter-system handover.
Among the required information, particularly the UTRAN capabilities (parameters specifying the extent to which the mobile radio subscriber appliance is UMTS-compatible) specific to the mobile radio subscriber appliance represent a significant volume of data (compared with the other signaling data).
In the course of the development for performing packet-switched inter-system handover, carried out as part of the 3GPP (Third Generation Partnership Project) standardization work, no solution has currently been provided for the problem of transmitting the required information. There are currently two proposals:
1. The mobile radio subscriber appliance transmits the required information as part of the GMM (GPRS Mobility Management; GPRS: General Packet Radio Service) registration request messages, that is to say using an Attach Request message or a Routing Area Update Request message, to the SGSN (Serving GPS Support Node) associated with the mobile radio subscriber appliance in the core network of the GSM mobile radio network. The SGSN stores the information and forwards it to the GERAN.
A drawback of this procedure is that the mobile radio subscriber appliance has no information about whether the GSM mobile network supports packet-switched inter-system handover to a UMTS mobile radio network, and the information is therefore always transmitted and forwarded, even if the GSM mobile radio network does not support packet-switched inter-system handover to a UMTS mobile radio network. In addition, this means that the information is repeatedly transmitted to the SGSN unnecessarily when the location within the SGSN's territory changes.
2. The GERAN node, that is to say the BSC associated with the mobile radio subscriber appliance in the GERAN, uses the RLC/MAC signaling radio link to request the required information from the mobile radio subscriber appliance immediately before the packet-switched inter-system handover to the UMTS mobile radio network is carried out.
The mobile radio subscriber appliance transmits the required information to the GERAN node using the RLC/MAC signaling radio link.
A drawback of this procedure is that the conventional RLC/MAC protocol allows only small volumes of data to be transmitted (25 octets per message), which is not sufficient for transmitting the required information. Extending the RLC/MAC protocol so that the mobile radio subscriber appliance can transmit specific information is involved and complex. In addition, the request for the required information immediately before the inter-system handover (a just-in-time request) increases the probability that the inter-system handover will fail or that errors will occur, since a significant delay can arise. In addition, this procedure requires the information to be transmitted using the radio interface upon each inter-system handover, which results in significant signaling involvement.
WO 02/01895 A1 discloses a method in which the information about the compression algorithms supported by a mobile radio subscriber appliance is transmitted to an RNC (Radio Network Controller) when a radio bearer is set up.
EP 1494494 A2 discloses a method for handover of a terminal to a UTRAN in which a mobile terminal transmits information to the UTRAN which relates to handover of circuit-switched communication links, and transmits no information relating to handover by packet-switched communication links.